I have just tried to engrave something in an aluminium plate (50x20 mm).
I was not very confident on having a good result, but to my surprise it finally came out quite good.
I used a black edding 500 permanent marker pen to paint the surface to engrave first, let it dry for 1/2 min (yes, I hace no patience at all 😅) , then engraved and to finish I used solvent and a soft cloth to remove the black paint.
black edding 500 permanent marker pen
As you can see in the photos below there is not much difference when using different speeds. I also tried with 2 passes and still not much difference.
Hope it helps for your future engravings!!